Gina Rinehart's Hancock Prospecting has been ordered to pay legal costs to Fairfax Media journalist Adele Ferguson after losing a long-running legal battle for the senior reporter to disclose her news sources.

The Western Australian Supreme Court also awarded special costs to Ms Ferguson - effectively removing the normal restrictions in calculating legal costs - given the complexity of the case.

Mining billionaire Mrs Rinehart ranks as the single largest shareholder in Fairfax Media, which owns publications including The Age, The Sydney Morning Herald and the Financial Review.

Gina Rinehart in Parliament House in Canberra in 2013. Photo: Andrew Meares

In March last year Mrs Rinehart's privately-held Hancock Prospecting issued a subpoena to Ms Ferguson requiring her to produce documents as part of the Walkley Award winning reporter's coverage of a bitter Rinehart family legal feud.

That subpoena also followed a similar subpoena made against West Australian newspaper journalist Steve Pennells demanding he also reveal sources that he relied on for reporting the Mrs Rinehart battle with two of her children. The move against Ms Ferguson drew heightened attention given she was the author of an unofficial Mrs Rinehart biography.

But both subpoenas were dismissed late last year following the introduction of new shield laws in Western Australia, aim at protecting journalists from revealing sources.

But a key argument by Hancock was the Western Australia shield laws did not apply to subpoena's issued before the new rules came into effect in late 2012.

Still, Justice Janine Pritchard ordered that the subpoena be set aside on the ground it was oppressive and an abuse of process.

She found that the shield laws applied, even though they came into operation after the subpoena was issued.

In making a ruling for special costs to be paid to Ms Ferguson, Justice Pritchard said the operation of Western Australia's new shield laws involved considering complex legal issues.

“The meaning and operation of the shield laws, and their relevance…involved novel and complex legal questions,” Justice Pritchard said in her cost finding.

She said the operation of the shield laws had still not been resolved when it came to considering the subpoena against Ms Ferguson even though the laws had also been considered as part of the proceedings against Mr Pennells.